Limits? What Limits? I.Q. and Brain Research

Many people think of intelligence as having a fixed genetic component that flourishes or fades with environmental influences like home life or economic opportunity. In this view, if children make the most of education, their developed intelligence can shine, but “innate” ability (as measured by I.Q.) still places a firm limit on how far they can go.

Recent discoveries suggest that this model is faulty, that the brain continues to develop physiologically after birth, discarding less useful synapses while strengthening more useful ones. The process continues into adulthood, making inherited and learned ability indistinguishable in any practical sense.

“From Neurons to Neighborhoods,” a new report from the National Academy of Sciences, summarizes the recent research. But Jack P. Shonkoff, its co-editor, a pediatrician who is dean of the Heller Graduate School of public policy at Brandeis University, cautions against simplistic efforts to enhance brain functioning. He doesn’t put much stock in fads like giving classical music CD’s to parents of newborns.

“Although it can’t hurt, there is nothing in brain research to support that,” Dr. Shonkoff said. “But there is a lot of hard science that tells us how to prevent harm.”

Brain development is inhibited by poor nutrition, toxins in the environment and a stressful or chaotic upbringing. It requires paying as much attention to early child care and education, beginning in infancy, as we now pay to kindergarten on up.

“Not more attention,” Dr. Shonkoff said, “but not less.” Smaller classes and more qualified teachers are good reforms for children in elementary schools, he notes, but they are just as crucial for children before they start kindergarten.

The nature-nurture dichotomy has been dealt a blow not only by brain research but also by a surprising long-term rise in average I.Q. scores.

Because exclusively genetic traits take eons to evolve, one might suppose that the current range of innate intelligence must be the same as in recent generations. But in the early 1980’s, James R. Flynn, a political scientist in New Zealand, made a remarkable discovery: average I.Q.’s rose by about three points a decade during most of the 20th century.

“The Rising Curve” (American Psychological Association, 1998), edited by Prof. Ulric Neisser of Cornell University, tries to explain this “Flynn effect.” One chapter notes, for example, that average height has increased even though it is strongly influenced by genes. If better nutrition created conditions for genes to increase height, other environmental improvements may be helping intelligence to flourish.

I.Q. seems to improve with more time in school. Professor Neisser’s book notes that in isolated areas where the gene pool has been unaffected by migration, the longer that children attend school, the higher their I.Q.’s on average. But more schooling can’t be a full explanation, because I.Q.’s have also risen for preschool children.

Rapidly changing urban surroundings and exposure to more complex stimuli may also enhance intelligence. Adults often joke about asking a child to program the VCR, saying he didn’t have to learn because “it must be in his genes.” But in a sense this may be no joke: a child could be more intelligent in this way because of how his environment has allowed his brain to develop physiologically.

Dr. Shonkoff speculates that average I.Q. may have risen because since the publication of Benjamin Spock’s “Baby and Child Care” in 1946, parents of all social classes have probably been more attentive to individual children’s particular needs.

The National Academy of Sciences report sees the brain as more plastic than “hard wired.” The manner of nurturing can raise or lower the limits of I.Q. This makes conditions in which children are reared, from the prenatal stage to adolescence, more crucial because (as with height) an interaction of genes and environment, not genes alone, produces potential as well as developed intelligence.

Dr. Shonkoff says the most nurturing environments build on tendencies already existing in the brain. And some environments exacerbate natural vulnerabilities that can limit I.Q. How well parents or other adults can “read” and respond to a child’s unique tendencies appears to be one measure of the way that genes and environment interact. For instance, adults may respond to a child genetically predisposed to inquisitiveness in a way that is different from their response to a child less naturally inquisitive. Adjusting this response may give the latter an equal chance for high intelligence.

If child care quality and the economic conditions affecting young children improve, along with regular school quality, a long-term rise in average I.Q. might continue.

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